Optical storage media light beam positioning system

ABSTRACT

An optical tracking system 10 is provided which comprises a beam source 12 which generates a light beam. The light beam travels through a splitter/filter 14 and proximate a DMD array 16. The DMD array 16 is controlled by a DMD array control system 18 which causes a single element within the DMD array to deflect the light beam towards a selected track on an optical storage medium 22. The optical storage medium 22 reflects the beam dependent upon the data stored on the selected track. The reflected beam is deflected by the DMD array 16 back to the splitter/filter 14 which separates the reflected beam from the impinging beam and directs the reflected beam to a detector 24 which discerns the information stored in the storage medium 22 responsive to the receipt of the reflected beam.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of electronic systems andmore particularly, the present invention relates to a method andapparatus for positioning a beam of light on a surface of an opticalstorage medium.

BACKGROUND OF THE INVENTION

The ability to efficiently store and retrieve data is an essentialcomponent of any integrated electronic system. In recent years, thedevelopment of optical storage systems has allowed greater storagedensities than previously known. An important concern of any storagemedia, including optical storage media, is the time required to accessthe storage system to either store or retrieve data.

Optical storage media are currently used in a variety of forms. Opticaldisks, rectangular optical media, and optical tape are some of theseforms. In each of these forms of optical storage media, a laser is usedto write and read from the optical storage media. In general, the beamof light is directed from laser to the surface of the optical storagemedia where it is reflected. The reflected beam of light is routed to adetector which can read the data stored on the optical storage mediaresponsive to the receipt of the reflected beam.

The methods and apparatus used to direct the beam of light to theappropriate section of the optical storage media are by far the slowestportion of the data storage and recovery system. For example, thetypical optical storage disk drive available currently have on the orderof 35 to 100 millisecond access times and additionally a rotationallatency of approximately 16 milliseconds. In comparison, the controllersassociated with these systems are working with an overhead ofapproximately one milli-second. Accordingly, there is approximately atwo order of magnitude difference between the mechanical access time ofthe optical storage drives and the remaining circuitry necessary toaccess data from the storage media. The primary reason for the slownature of, for example, an optical storage disk drive, is the timerequired to mechanically position the optics which are used to directthe beam of light to and from the appropriate positions on the surfaceof the optical storage media. An additional factor increasing the accesstimes of optical storage disk drives is the rotational latency of thedisk as it turns to bring the desired portion of the disk proximate thereading optics. Most current systems use a carriage assembly which holdsvarious mirrors and optics and which is mechanically positioned over asection of the optical storage disk, for example. Data accessing mustthen wait for the optical disk to mechanically rotate to the desiredsection. The positioning of these carriage assemblies accounts for thefirst order term of the delay in accessing the optical storage media.The rotational latency accounts for the second order delay term.

Accordingly, a need has arisen for an optical tracking system whicheliminates the need for the mechanical positioning of a carriageassembly and/or eliminating rotational latency and therefore reduces thetime required to access the data stored in an optical storage media.

SUMMARY OF THE INVENTION

In accordance with the present invention, an optical tracking system isprovided which substantially eliminates or reduces disadvantages andproblems associated with prior optical storage accessing systems.According to one embodiment of the present invention, an opticaltracking system is provided which comprises a deformable mirror devicearray also known as digital micromirror devices (DMDs). A beam of lightis generated and directed proximate the surface of the DMDs array. Aparticular DMDs within the array may be deflected into the path of thelight beam while non-deflected elements within the array will allow thebeam to pass over them. The deflected element within the DMDs array willdeflect the light beam to a selected track within an optical storagemedium. Conventional beam splitters, optical filters and detectors areused to read the data from the reflected beam. An array control systemis provided to select the particular DMDs.

According to another embodiment of the present invention, a light beamsource generates a light beam which is widened such that it illuminatesthe entire DMDs array. A single DMDs within the array can be deflectedto select a particular track on the optical storage medium associatedwith that DMDs. The selected DMDs directs a portion of the widened beamto the selected track on the optical storage medium which reflects thebeam according to the data stored in that track of the optical storagemedium. Control systems and detection systems are provided as describedpreviously.

An important technical advantage of the present invention inheres in thefact that the DMDs array systems provide extremely fast access toparticular tracks within an optical storage medium without requiring thecumbersome movement of mechanical carriage assemblies, common in prioroptical tracking systems. A further important technical advantage of thepresent invention inheres in the fact that the DMDs arrays can bemanufactured using semiconductor processes to provide for an extremelyefficient, reliable and inexpensive high quality reflective surfacewhich is selectable using conventional semiconductor addressingtechniques and circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be acquiredby referring to the detailed description and claims when considered inconnection with the accompanying drawings in which like referencenumbers indicate like features, and wherein:

FIG. 1 is a schematic diagram of one embodiment of the optical trackingsystem of the present invention;

FIG. 2 is a schematic diagram of a second embodiment of the opticaltracking system of the present invention; and

FIG. 3 is a cross-sectional schematic diagram of a single deformablemirror device which may be used in conjunction with the optical trackingsystem of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an optical tracking system constructed according tothe teachings of the present invention is indicated generally at 10.System 10 comprises a light beam source 12 which is operable to generatea light beam and transmit the light beam through a splitter/filter 14.The light beam issues from splitter/filter 14 and travels proximate thesurface of a deformable mirror device, also known as digital micromirrordevice [DMD] array 16. DMD array 16 may comprise, for example, a lineararray of deformable mirror devices which are capable of angulardeflection on the order of plus or minus 9 degrees when an individualelement is selected through an addressing system integral with the DMDarray 16. The selection and addressing of the particular elements withinthe DMD array 16 is controlled by a DMD array control system 18.

DMD arrays, such as DMD array 16, are known in the art and have beenapplied in such applications as printers. A complete description of asuitable DMD array may be found in U.S. Pat. No. 4,596,992 issued toHornbeck entitled, "Linear Spatial Light Modulator and Printer". Apossible embodiment of the elements of DMD array 16 will be describedmore fully with reference to FIG. 3 herein. It should be understood thatthe description of the present invention using an array of DMD's issolely for the purpose of teaching important technical advantages of thepresent invention and should not be construed to limit the presentinvention to this or any embodiment. For example, the system of thepresent invention could use other methods of controlling a light beamsuch as an array of conventional mirrors or a fiber optic arraycontrolled with EMI fields. These and other embodiments are intended tobe included within the scope of the present invention.

In operation, DMD array 16 functions to selectively deflect the beam oflight through a system of correction optics 20 and on to a selectedtrack within an optical stored medium 22. Optical storage medium 22 maycomprise, for example, an optical storage disk which rotates at asuitable rate to allow for the efficient access of information storagepositions on the surface of the medium 22. The optical storage medium 22reflects the beam of light according to the data stored on its surfaceand the beam of light returns through correction optics 20 and isdeflected back to splitter/filter 14 by the particular element selectedwithin DMD array 16. The splitter/filter 14 separates out the reflectedbeam from the impinging beam using known methods and directs thereflected beam to a detector 24 which is operable to discern theinformation stored in the selected track of optical storage medium 22responsive to the receipt of the reflected beam from splitter/filter 14.

It should be understood that while the DMD array 16 is shown having onlya small number of individual elements, in actual practice DMD array 16could have an extremely large number of individual elementscorresponding to a one-for-one relationship between the number of DMDelements within the array 16 and the number of tracks desired to beaccessed on optical storage medium 22 at any one time. According to oneembodiment, DMD array 16 could have as many individual elements as thetotal number of tracks in optical storage medium 22. According to thisembodiment, the DMD array 16 could provide almost instantaneous accessto any track in optical storage medium 22 without having to repositionDMD array 16 relative to optical storage medium 22.

If a one-for-one relationship between the number of elements in DMDarray 16 and the number of tracks desired to be accessed on opticalstorage medium was not practical because of the particular physicalconstraints of a particular application, DMD array 16 could have asmaller number of elements than the total number of tracks on opticalstorage medium 22. The DMD array 16 would then have to be repositionedwhenever a track was desired to be read from optical storage medium 22that did not fall within the current accessing capability of the currentposition of the DMD array 16. While this configuration would stillrequire a mechanical movement of a carriage assembly comprising DMDarray 16, it would still be an improvement over current systems in thata plurality of tracks could be accessed from any one mechanicalpositioning of the DMD array 16. Accordingly, the number of mechanicalpositionings would be greatly decreased and a coresponding decrease inthe average access time would result. The repositioning of DMD array 16necessary for this embodiment could be accomplished using conventionalcarriage assemblies known in the art.

DMD array 16 is shown with its individual elements in a linearrelationship to one another. It should be understood that the density ofthe tracks on any particular optical storage medium 22 may requirestaggering of the elements within the DMD array 16 into two or possiblyeven more rows of individual elements. Conventional optical techniquescan be used to provide a beam of light passing over each element withinDMD array 16 regardless of the actual number of rows used within DMDarray 16.

Further, while the schematic illustration of system 10 in FIG. 1indicates that the particular elements within DMD array 16 would allhave constant deflection, it should be understood that the particularelements within DMD array 16 may have variable deflections within thearray 16. For example, the maximum deflection of an element at one endof the array 16 might be much larger than the maximum deflection of anelement at the opposite end of array 16 depending upon the requiredspacing and positioning of the physical elements within the opticaltracking system 10.

Referring to FIG. 2, a second possible embodiment of the opticaltracking system of the present invention is indicated generally at 25.System 25 is similar to system 10 illustrated in FIG. 1 and comprises abeam source 12, a splitter/filter 14, a DMD array 16, a DMD controlsystem 18 and correction optics 20. System 25 similarly reads datastorage positions on an optical storage medium 22 through the use of adetector 24. System 25 differs from system 10 in that it also comprisesa beam widener 27. Additionally, the orientation of the impinging beamon DMD array 16 is different than that in system 10. According to theoperation of system 25, a beam is received from splitter/filter 14 bybeam widener 27 which functions to illuminate the entire surface of DMDarray 16. A single element within DMD array 16 may be deflected in sucha manner that only a single track on optical storage medium 22 iscontacted by the reflected beam. The remaining elements within DMD array16 deflect the light received from beam widener 27 away from thecorrection optics 20 and the optical storage medium 22. In this manner,a single track of optical storage medium 22 may be selected by thedeflection of a single element within DMD array 16.

The reading of data by detector 24 is accomplished in a similar manneras discussed previously with respect to system 10 of FIG. 1. DMD array16 is shown in FIG. 2 to have the non-selected elements within the arrayin a deflected orientation while the selected element is substantiallyparallel to the surface of array 16. It should be understood that thismethod of operation is merely one possible embodiment of the presentinvention and depending upon the orientation of beam source 12, array 16and optical storage medium 22, various orientations and deflectionscould be used for the non-selected elements and the selected elements.These other orientations are intended to be included within the scope ofthe present invention and the selection of the orientation shown insystem 25 is merely for the purpose of teaching the present invention.It should also be understood that the comments made within respect tosystem 10 of FIG. 1 having to do with the staggering of the elementswithin DMD array 16 as well as the variable deflection possibilitieswithin DMD array 16 are equally applicable to system 25. In addition,DMD array 16 may or may not contain a number of elements equal to thetotal number of tracks within optical storage medium 22. As discussedpreviously, DMD array 16 could be used to define and provide almostinstantaneous access to a predetermined number of tracks within opticalstorage medium 22 and still greatly improve on the access timescurrently known.

FIG. 3 is a cross-sectional schematic diagram of a deformable mirrordevice which could be used for the DMD elements within DMD array 16 inthe present invention. FIG. 3 illustrates a deformable mirror deviceindicated generally at 26. The deformable mirror device 26 may befabricated using known methods over a semiconductor substrate whichitself can incorporate an integrated CMOS address structure. As shown inFIG. 3, deformable mirror device 26 comprises an outer aluminum alloylayer 28 separated from the underlying CMOS address layers by asacrificial spacer layer 30. During the manufacture of DMD 26, a portionof the outer aluminum alloy layer 28 is removed by a metal etch step todefine a torsion beam 32. A torsion rod 34 is formed passing throughtorsion beam 32 and connecting it to the remainder of the outer layer28. The cross section shown in FIG. 3 is perpendicular to the long axisof torsion rod 34. After the torsion beam 32 has been defined by themetal etch step, the spacing material in layer 30 is removed beneath thetorsion beam 32 using an isotropic plasma etching step to form an airgap capacitor between the torsion beam 32 and the underlying addressstructure. The underlying address structure comprises a first landingelectrode 36, a second landing electrode 38 and first and second addresselectrodes 40 and 42 as shown in FIG. 3.

In operation, signals may be placed on first and second addresselectrodes 40 or 42 to rotate the torsion beam 32 about the torsion rod34. By placing appropriate signals on address electrodes 40 and 42, thetorsion beam 32 can be made to rotate in either direction until the endsof the torsion beam 32 nearly contact the landing electrodes 36 and 38.For example, a voltage can be placed on address electrode 42 tending toattract torsion beam 32 causing torsion beam 32 to rotate in a clockwisedirection. A second voltage may simultaneously be placed on addresselectrode 40 to repel torsion beam 32 to initiate the clockwiserotation. Similar signals may be used to achieve a counter-clockwiserotation of torsion beam 32. Conventional signal processing techniquescan be used to generate the required voltages and timing of the signalsto be placed on address electrodes 40 and 42.

Using known methods, a deformable mirror device such as deformablemirror device 26 can be constructed to have a maximum deflection of thetorsion beam 32 of plus or minus 9 degrees from horizontal. As discussedpreviously, other angles of deflection may be useful at various pointsin the array 16. These other angles can be accomplished by altering thespacing between the landing electrodes 36 and 38 and torsion beam 32.The individual elements within DMD array 16 can also be controlledlinearly using analog control signals to provide for various angles ofdeflection.

The torsion beam can respond to voltages placed on address electrodes 40or 42 in approximately 12 microseconds. This obviously represents asubstantial improvement over the 35 to 100 millisecond response timescommon in the present tracking systems available. The aluminum alloyused to manufacture torsion beam 32 provides a superior mirror surfaceto prevent any distortion of the beam received from splitter/filter 14and generated by beam source 12. Further, the small area occupied by andmass of the torsion beam 32 allows for extremely quick reaction time andequally rapid access time to the data storage positions in opticalstorage medium 22. For example, a typical size for torsion beam 32 wouldbe on the order of approximately 0.55 square mils. The use of suchmicromechanical structures provides a optical tracking system which doesnot require the movement of the large masses involved in prior carriageassemblies.

Accordingly, through the use of DMD array 16 containing a predeterminednumber of individual elements such as DMD 26 described in FIG. 3, anoptical tracking system is provided which allows for dramaticallyimproved access times relative to currently available tracking systems.The DMD array can be oriented so that only the selected element deflectsthe light beam towards the optical storage media such as was describedwith reference to system 10 in FIG. 1 or the DMD array can be orientedsuch that all of the elements are illuminated by the impinging beam andonly the selected element within the array directs a beam towards theoptical storage medium such as described with reference to system 25 inFIG. 2. As discussed previously, the array 16 can be sized such thatthere is a single element corresponding to each track within the opticalstorage medium or the array can contain a smaller number of elementsthan tracks in the storage medium. If there is a smaller number ofelements than the number of tracks, the array assembly or the opticalstorage media may be moved periodically to provide access to every trackon the optical storage medium. According to this embodiment, the almostinstantaneous access to a plurality of tracks on the optical storagemedia at any one time allows for a reduced number of mechanicalmovements necessary and thereby a corresponding decrease in the averageaccess time for the system as a whole.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed is:
 1. An optical tracking system of directing a beam oflight used to access an optical storage medium, comprising:a light beamsource for generating a beam of light; an array control system forselectively transmitting a deflection signal; an array comprising aplurality of mirror elements, each of said mirror elements formed on acommon substrate and comprising a mirrored outer surface and an addresselectrode disposed inwardly from said mirrored outer surface, saidaddress electrode for receiving said deflection signal, said deflectionsignal for deflecting said mirrored outer surface, wherein said beam oflight is reflected by said mirrored outer surface to form an impingingbeam; an optical storage medium wherein said impinging beam is reflectedby said optical storage medium to create a reflected beam; and adetector disposed in the path of said reflected beam and operable todiscern the data stored on the optical storage medium responsive to thereceipt of said reflected beam.
 2. The system of claim 1 wherein saidimpinging beam and said reflected beam have substantially coincidentpaths, the system further comprising a beam splitter disposed in saidcoincident paths and operable to direct said reflected beam to saiddetector.
 3. The system of claim 1 wherein said optical storage mediumcomprises a number of tracks, each of said tracks comprising a pluralityof data storage locations, said array having a number of elements notless than said number of tracks such that each of said tracks isassociated with one of said elements.
 4. The system of claim 1 whereinsaid optical storage medium comprises a number of tracks, each of saidtracks comprising a plurality of data storage locations, said arrayhaving a number of elements less than said number of tracks such thatnot all said tracks are accessible from a single position of said array,said array control system comprising:an array positioning systemoperable to position said array relative to the optical storage mediumsuch that each of said tracks may be selectively accessed.
 5. The systemof claim 1 wherein said array control system comprises circuitry forindependently and selectively activating an address electrode associatedwith each of said elements.
 6. The system of claim 1 and furthercomprising a beam widener disposed in the path of the beam between saidlight beam source and said array and operable to widen the beamgenerated by said source such that said widened beam simultaneouslyimpinges on each element in said array.
 7. The system of claim 1 whereinsaid mirror elements comprising:a torsion beam having a mirrored outersurface; and a torsion rod coupling said torsion beam to saidsubstrate;wherein said deflection signal is operable to rotate saidtorsion beam about said torsion rod.
 8. An optical tracking system fordirecting a beam of light used to access an optical storage medium,comprising:a light beam source for generating the beam; an arraycomprising a linear array of deformable mirror devices formed on asubstrate, each of said deformable mirror devices comprising a torsionbeam having a mirrored outer surface, a torsion rod coupling saidtorsion beam to said substrate, and an address electrode disposedinwardly from said mirrored outer surface, said address electrode forreceiving a deflection signal; an array control system operable forselectively transmitting said deflection signal to said addresselectrode; a beam widener disposed in the path of the beam between saidlight beam source and said array and operable to widen the beamgenerated by said source such that said widened beam impinges on each ofsaid elements in said array; and said optical storage medium operable toreflect the beam, a detector disposed in the path of said reflected beamand operable to discern the data stored in the selected portion of theoptical storage medium responsive to the receipt of said reflected beam.9. The system of claim 8 wherein said array control system comprisescircuitry for independently and selectively activating an addresselectrode associated with each of said elements.